This invention relates in general to electrostatography and, more specifically, to an electrostatographic imaging member having a charge transport layer comprising a charge transport material containing a dendrimeric molecule structure
In the art of electrophotography, an electrophotographic plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation such as light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper.
Electrophotographic imaging members are usually multilayered photoreceptors that comprise a substrate support, an electrically conductive layer, an optional charge blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional protective or overcoating layer(s). The imaging members can take several forms, including flexible belts, rigid drums, etc. For many multilayered flexible photoreceptor belts, an anti-curl layer is usually employed on the backside of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoreceptor flatness.
Various combinations of materials for charge generating layers and charge transport layers have been investigated. U.S. Pat. No. 4,265,990 discloses a layered photoreceptor having a separate charge generating (photogenerating) layer (CGL) and charge transport layer (CTL). The charge generating layer is capable of photogenerating holes and injecting the photogenerated holes into the charge transport layer. The photogenerating layer utilized in multilayered photoreceptors include, for example, inorganic photoconductive particles or organic photoconductive particles dispersed in a film forming polymeric binder. Inorganic or organic photoconductive materials may be formed as a continuous, homogeneous photogenerating layer. The disclosure of this patent is incorporated herein by reference.
Examples of photosensitive members having at least two electrically operative layers including a charge generating layer and diamine containing transport layer are disclosed in U.S. Pat. Nos. 4,265,990, 4,233,384, 4,306,008, 4,299,897 and 4,439,507. The disclosures of these patents are incorporated herein in their entirety. Charge transport layers are known to be comprised of any of several different types of charge transport material dispersed in a polymer binder.
U.S. Pat. No. 4,806,443 describes a charge transport layer including a polyether carbonate (PEC) obtained from the condensation of N, Nxe2x80x2-diphenyl Nxe2x80x2-bis(3-hydroxyphenyl)-[1,1xe2x80x2-biphenyl]-4,4xe2x80x2-diamine and diethylene glycol bischloroformate. U.S. Pat. No. 4,025,341 similarly describes that a photoreceptor includes a charge transport layer including any suitable hole transporting material such as poly(oxycarbonyloxy-2-methyl-1,4-phenylenecyclohexylidene-3-methyl-1,4-phenylene.
In multilayer photoreceptor devices, one property, for example, is the charge carrier mobility in the transport layer. Charge carrier mobility determines the velocities at which the photo-injected carriers transit the transport layer. For greater charge carrier mobility capabilities, for example, it may be necessary to increase the concentration of the active molecule transport compounds dissolved or molecularly dispersed in the binder. Phase separation or crystallization sets an upper limit to the concentration of the transport molecules that can be dispersed in a binder. What is still desired is an improved material for a charge transport layer of an imaging member that exhibits excellent performance properties and has a further advantage of not being susceptible to crystallization when present in the charge transport layer at a level of from about 30 weight percent or higher.
Disclosed herein is an electrophotographic imaging member comprising a supporting substrate,
a charge blocking layer,
an optional adhesive layer,
a charge-generating layer,
a charge transporting layer,
a binder,
a charge transporting compound for use in a charge transport layer of an imaging member, and
a charge transport layer material that is capable of not crystallizing at a weight percentage of from about 50 percent or higher.
Further disclosed is a charge transport material with a single carbon cored dendrimeric, star-like molecular structure that usually does not exhibit early onset of charge transport layer fatigue cracking. By the use of the disclosed dendrimeric materials in the charge transport layer of the present invention, a charge transport layer of an imaging member is achieved that has excellent hole transporting performance, less crystallization, and better wear resistance, and is able to be coated onto the imaging member structure using known conventional methods.
Aspects illustrated herein relate to an imaging member comprising, for example, a flexible supporting substrate,
a charge blocking layer,
an optional adhesive layer,
a charge-generating layer,
a charge transporting layer comprising an electron transport molecule with a single carbon cored dendrimeric, star-like molecular structure, and
a binder.
The charge transport layer of a photoreceptor must be capable of supporting the injection of photo-generated holes and electrons from a charge generating layer and allowing the transport of these holes or electrons through the organic layer to selectively discharge the surface charge. If some of the charges are trapped inside the transport layer, the surface charges will not completely discharge and the toner image will not be fully developed on the surface of the photoreceptor.
The charge transport layer thus includes at least one charge transport material. For example, in embodiments, a charge transport molecule comprises a single carbon cored dendrimeric star-like compound represented by: 
wherein Z1-4 is independently selected from: 
wherein
R1, R2, R3 and R4 are independently selected from xe2x88x92CnH2n=1 wherein n is an integer from 0 to 6,
Ar1, and Ar2 are independently selected from: 
wherein Y1 to Y5 are independently selected from hydrogen, halogen, alkyl, alkoxy, thioalkoxy, cyano, amino, carboxylic acid, mono- or di-substituted amino, hydroxy, mercapto, aryloxy, arylthio, carbocyclic aromatic ring group and heterocyclic aromatic ring group.
Typical dendrimeric compounds are represented by: 
For example, in embodiments the charge transport layer comprises from about 20 to about 80 percent by weight of at least one charge transport material and about 80 to about 20 percent by weight of a polymer binder. The dried charge transport layer can contain from about 30 percent and about 70 percent by weight of a charge transport molecule based on the total weight of the dried charge transport layer.
The charge transport layer material may also include additional additives. Such as, for example, antioxidants, leveling agents, surfactants, wear resistant additives such as polytetrafluoroethylene (PTFE) particles, light shock resisting or reducing agents, and the like.
The solvent system can be included as a further component of the charge transport layer material. A number of conventional binder resins for charge transport layers have utilized methylene chloride as a solvent to form a coating solution, for example that renders the coating suitable for application via dip coating. However, methylene chloride has environmental concerns that usually require this solvent to have special handling and results in the need for more expensive coating and clean-up procedures. Currently, however, binder resins can be dissolved in a solvent system that is more environmentally friendly than methylene chloride, thereby enabling the charge transport layer to be formed less expensively than with some conventional polycarbonate binder resins. In embodiments a solvent system for use with the charge transport layer material of the present invention comprises tetrahydrofuran, toluene, and the like.
The total solid to total solvents of the coating material may for example, be around about 10:90 weight percent to about 30:70 weight percent, and in embodiments from about 15:85 weight percent to about 25:75 weight percent.